The heliobacteria are phototrophic, that's to say, they convert light energy into chemical energy by photosynthesis; they use a PSI type reaction center. The primary pigment involved's bacteriochlorophyll g, which's unique to the group and has a unique absorption spectrum; this gives the heliobacteria their own environmental niche. Phototrophy takes place at the cell membrane, which doesn't form folds or compartments as it does in purple phototrophic bacteria. RNA trees place the heliobacteria… (More on Heliobacteria)